Many proteins are dependent upon chaperones to properly fold. Failure to fold correctly is associated with many diseases including cancer and aging associated neurodegenerative disorders. While most chaperones are redundant in function, TRiC and its homologous chaperonins are essential in all kingdoms. All eukaryotic chaperonins are composed of two rings stacked back to back, each formed by 7-9 subunits that produce a central cavity that encapsulates substrates. TRiC-mediated folding is driven by ATP binding and hydrolysis, which regulate its conformational cycle. While progress has been made in understanding the mechanism of simpler homo-oligomeric archaeal chaperonins, the mechanism of folding by the eukaryotic chaperonin, TRiC, which is composed of eight paralogous subunits, has remained elusive. Importantly, the divergence of the subunits has provided unique folding properties allowing TRiC to fold essential eukaryotic substrates that the homologous chaperonins are incapable of folding. TRiC is also assisted by the hetero-hexameric cochaperone Prefoldin, which is thought to transfer non-natively folded substrates to TRiC. The goal of this proposal is to study mechanistic, functional and structural aspects of the ATP-dependent conformational cycle of TRiC and the mechanisms of TRiC substrate-recognition; I also aim to define whether and how these TRiC functions are modulated by Prefoldin. The Frydman lab has developed a system in yeast that allows replacement of any of the TRiC subunits with the same subunit containing lethal mutations, and has extensive experience and tools to address these questions in vivo and in vitro.